1. Field of the Invention
The present invention relates generally to the disposal of oily sludge. More specifically, the present invention relates to an apparatus and method for the biological degradation of oily sludge with the apparatus comprising a sequencing batch reactor for the on-site degradation of oily sludge.
2. Description of the Prior Art
Biological treatment facilities and processes are increasingly used to treat a wide variety of organic rich waste streams. The most common application of biological treatment of waste is sewage treatment. Food processors, feed lots, the paper industry, oil refineries, and the automotive industry often use on-site biological treatment processes for high biological demand waste. In most applications, biological treatment facilities/systems are designed to promote the growth of naturally occurring bacteria adapted to grow on and degrade the targeted waste. The basic requirements are that the system be well mixed, maintain a near neutral pH, and for most applications operate aerobically. To reduce the amount of residual biomass and to generate methane which is captured and used as fuel, some waste streams are treated anaerobically by biological treatment systems. To accommodate the longer residence times needed to treat waste anaerobically, the capacity of the treatment system is often much larger than a corresponding aerobic system. When treating industrial waste as opposed to sewage, nitrogen, phosphorus, and low concentrations of vitamins are added to promote bacterial growth. In recent years, technological enhancements, e.g., trickling filters, rotating bio contactors, and activated sludge systems have been developed to maximize bacterial contact with the waste and reduce processing time for treating the waste. For most applications a simple stirred tank reactor is sufficient.
Biological treatment will remove more than ninety percent of suspended organic solids and it is the most cost effective treatment available for dissolved organics. Although significant progress has been made in treating compounds once considered recalcitrant, biological treatment of some organic pollutants, such as PCB's is not yet practicable. High concentrations of heavy metals, solvents, salt, and extremes of pH or temperature will hinder and in some cases poison biological treatment systems. These effects are usually transient and systems rapidly recover when normal conditions are restored.
Vigorous aeration of a treatment reactor produces air emissions and the degradation process itself may produce volatile compounds. These compounds are usually biodegradable and one treatment process currently being used passes exhaust air through containers filled with compost, this process being known as biofiltration. Bacteria in the compost capture and degrade volatile hydrocarbons and some inorganic species, e.g., hydrogen sulfide and ammonia. Biological treatment produces a residue that is primarily biomass, i.e., bacteria and cell remnants. The volume depends on the capacity of the system and the residence time in the reactor. Since biomass is recycled and broken down during each reactor cycle, the total amount of biomass increases slowly. Most industrial applications produce 1 to 2% of reactor sludge per gallon of treated oily wastewater. Unless the concentration of metals exceeds allowable limits, the residue is usually non-toxic and non-hazardous and can be captured in a filter press, bag filter, landfarmed, landfilled, or composted.
Department of Defense (DOD) military facilities generate thousands of tons of oily sludge annually at industrial wastewater treatment plants, wash racks, fuel depots, industrial operations, and maintenance facilities. Since oily sludge cannot be recycled or burned, it is drummed and stored at landfills. The disposal cost to the Department of the Navy is in excess of $6.5 M per year. Due to increasing costs, long-term liability, and restrictions on landfill disposal, there is an urgent need for a cost effective on-site treatment.
Navy research efforts concluded that bacteria already present in and adapted to oily sludge from a variety of sources degrade the hydrocarbons found in oily sludge within 2 weeks from 20,000 ppm to less than 100 ppm. In addition, research found that the concentrations of heavy metals, which are primarily zinc and copper, and total suspended solids in treated sludge residuals were well below mandated discharge limits. The results of the research demonstrated that on-site biological treatment was technically and economically feasible to the Military.